Means for airplane approach control



Jan. 17, 1950 s, SAINT 2,495,139

MEANS FOR AIRPLANE APPROACH CONTROL Holding Stack 1T5 AP4 3000 APa APZ 2000 API I X3 X3134 Rwi 1T2 IT5\ N L K v Z Id finnfntor 7 By MMM w (Ittorneg Jan. 17, 1950 s. P. SAINT MEANS FOR AIRPLANE APPROACH coNTRbL 5 Sheets-Sheet 3 Filed Dec. 22, 1944 owmo/ WQ Patented Jan. 1 7, 1950 OFFICE IVIEANS FOR AIRPLANE APPROACH CONTROL Samuel P. Saint, Port Washington, N. 2., assignor to General Railway Signal Company, Rochester, N. Y.

Application December 22, 1944, Serial No. 569,335

This invention relates to apparatus for landin airplanes in proper time spaced sequence from a holding stack in spite of the fact that airplanes stored by flying at different altitudes in such stack are not coordinated and therefore will require diiierent time periods to reach the exit point of such holding stack after having been called.

Holding stacks for storing airplanes have been used for some time and constitute paths in space over which airplanes may fly at assigned altitudes to consume time. These paths may be defined by well known landmarks such as roads and buildings, or by suitable markers or radio beacons to guide the pilot both during visibility and under load atmospheric conditions. The flying paths of such holding stacks may be of circular form or may constitute two semi-circles having their ends connected by straight lines, similar to a conventional race track, or may be of any other suitable configuration. In any event, the holding paths over which airplanes must fly during storage must be large enough so as to prevent banking of an extent which would make it uncomfortable for the passengers. If the flying pattern for the stack is circular, the circle should not be of smaller diameter than the diameter which requires two minutes of flying time to complete one round. For oblong holding stacks the circular portion is preferably a one-minute semi-- circle.

In accordance with the present invention, it is proposed to provide a holding loop for each of, say, the lower three altitudes of the holding stack which loop is of variable length and configuration so as to consume variable amounts of time for "ie purpose of landing the airplanes at the proper times, and is preferably, though not necessarily, located outside the holding stack.

The method employed in landing airplanes in accordance with the present invention resides in 40" an operator, preferably located on the ground, calling one or more airplanes at a specific time or times for landing purposes, in taking cognizance of the time the airplane leaves the holding stack for the purpose of determining how much time the pilot of such airplane is to consume in the variable length holding loop and the dimensions and configuration of such loop so as to bring the airplane to the entering end of the glide path for gliding down upon the landing strip at the predetermined time assigned to that airplane. If it is desired to land airplanes closer together than the total landing procedure time, then such airplanes must be called for landing procedures in overlapped relationship.

9 Claims. (Cl. 235-61) In accordance with the present invention, it is proposed to use either a computer or approximater to compute the time the pilot is to consume in the holding loop and the azimuth angle at which he is to fly by using suitable curves, tables, or other data for quickly arriving at the proper answers or if desired an operator or the pilot may commit certain facts to memory and solve for these factors in his mind.

In accordance with one form of the present invention, it is proposed to employ an oblong storage or holding stack and a pattern for the storage or holding loop which pattern consists of two radial flight lines terminating at the exit point of the holding stack and the other ends of which are connected by a one minute semi-circle. Obviously, a storage or holding loop of this configuration will result in a smaller angle between the two flight lines mentioned as these flight lines become longer, f or which reason it is not only necessary to calculate the time length of the flight line but it is also necessary to calculate the angle therebetween to determine the size of the storage loop which depends upon the total time to be consumed therein.

In accordance with another form of the invention the storage or holding stack is also oblong and in this form the storage or holding loop re sides merely in extending the length of the storage stack to the desired extent when an airplane is called from the storage stack. In this case as in others the storage stack is defined by physical dimensions chosen to fit suitable time dimensions whereas the storage loop is defined by time dimensions, especially under no-Wind condition.

In accordance with one form of the present invention, a computer may be employed which enables the desired factors to be obtained more quickly and which enables this information to be more accurately determined. This computer preferably includes a cylinder which may be r'o tated dependent upon the prevailing head or tail wind and which may be arranged adjacent a time tape by which the time read off of an ordinary clock face may be mentally transferred to the time tape to indicate on the cylinder a point corresponding to the time at a particular instant. It is also proposed to have associated with the cylinder above mentioned, a data strip which enables an angle to be read for the particular storage loop calculated by the cylinder apparatus so that the operator cannot only read an out-time figure which is the time to be consumed in the storage loop before he makes his procedure turn but may also read an angle which is such that a one minute semi-circle time distance will be available to the pilot in making his turn preceding his return flight. Obviously, the data on such cylinder may equally as well be on a plane surface which may be shifted to correspond to the turning of the roller. Such a data sheet has been shown in Fig. 6 of the drawings associated with a similar time tape and angle chart or data strip.

Other objects, purposes and characteristic features of the method and means of the present invention will in part be pointed out in the specification hereinafter and will in part be obvious from the accompanying drawings, in Which Fig. 1 illustrates a ground plan for a storage or holding stack and a variable length storage or holding loop having associated therewith radio beacons and a runway;

Fig. 2 shows a side elevation of the holding stack and holding loop illustrated in Fig. 1 and also illustrates how three different airplanes may make landings in overlapped relationship spaced substantially equal time periods apart and land upon the runway;

Fig. 3 shows a modified form of holding stack and holding loop in which the holding loop constitutes the extension of an oblong holding stack;

Fig. 4 ilustrates one form of computer for quick computation of the angle of flight for an airplane entering the holding loop shown in Fig. 1 and for calculating the distance, expressed in time, the airplane is to fiy out on the straight line portion of this holding loop;

Fig. 5 illustrates a cover, together with a clock therein, for the computer illustrated in Fig. 4;

Fig. 6 illustrates the chart constituting part of the roller of the computer illustrated in Fig. 4 of the drawings; and

Fig. 7 illustrates a holding loop drawn to a time scale where there is a prevailing head wind for north-bound flying.

StructuTeFig. 3.In Fig. 3 has been illustrated a plan view of a relatively simple flying pattern whereby the method of landing airplanes in accordance with the present invention may be practiced with a minimum or" mental computing. In this form of the invention several radio beacons RBI, BB2 and BB3 are preferably so located on the ground as to be useful in guiding the pilot under adverse visibility conditions in both the holding stack defined by these beacons and in the holding loop located outside the holding stack. It is of course understood that under favorable weather conditions the invention may be practiced by flying with respect to other land marks such as buildings and highways and without such beacons or other apparatus as will presently become apparent.

Ii radio beacons such as beacons RBI, R82 and BB3 are employed these beacons are preferably of the omni-directional type which beacons radiate radiant energy in every direction. It is naturally desirable to practice the method of spacing airplanes in accordance with the present invention by using the radio facilities currently available at airfields and for this reason conventional radio range stations which emit two rather wide beams of the same or different carrier frequency in overlapped relationship and of which one of these beams is coded to the letter A and the other is coded to the letter N so that if both beams are received, as they will if the airplane fiies over the overlapped portion thereof, known as the beam, these two codes will blend into each other to make one continuous hum; and other beacons such as fan markers and Z-markers may also be used if desired. It may be pointed out that a Z-marker is sometimes located in the silent cone portion of a radio range station and where that is the case the Z-marker will serve as an additional check of a manifestation that the airplane is flying directly over the radio range station.

It may be pointed out that the airplanes are preferably equipped with an automatic homing directional indicator so that as an airplane flies over an omni-clirectional radio beacon this direction finder will suddenly flip over so as to indicate that the beacon is no longer ahead of the airplane but is behind the airplane. The Z-marker which is a radio station which emits a vertically upwardly directed radio beam may cooperate with apparatus on the instrument board for lighting a small lamp when the airplane is directly over such Z-marker. Although specific apparatus which may be used as an adjunct to the present invention has been mentioned, it should be understood that this apparatus is not necessary under fair weather conditions and that under adverse weather conditions any suitable navigation facilities which are available may be used if desired in practicing the present invention. It may be pointed out that when omni-directional radio beacons are used they preferably have carrier frequencies ranging from 190 to 550 kilocycles.

Referring again to Fig. 3 of the drawings it may be pointed out that the radio beacons RB2 and I BB3 are preferably lined up with the runway RWI and that the holding stack SI and the holding loop Ll are preferably so proportioned that the minimum size holding loop will extend beyond the limits of the holding stack under the most adverse wind conditions such as a head wind which may cause the airplane to lose more time in the holding stack than would be ordinarily expected and that the largest holding loop is of such size, expressed in time consumed that all of the time to be consumed by the airplane may be consumed in this holding loop, such as loop Ll having an in-time 1T3, under the conditions where the airplane is called from the holding stack when it is near the exit end of the holding stack.

It may be pointed out that the holding stack is preferably of such size that the two semi-circles forming the ends of the oblong holding stack each require one minute to be traversed by an airplane flying at a speed of miles per hour and such that the straight line portions of this holding stack will be traversed in one minute of flying time under no wind conditions. With a holding stack of the time spacings just mentioned the holding loop is preferably of such size that when the maximum time of two minutes is consumed in the holding stack under no wind conditions the loop will have straight line portions which consume one minute each and will include a semi-circle which requires one minute of flying time. Other holding loops are proportionately larger as the stack loss times become smaller. The total time between calling of an airplane from the stack and its completion of the holding loop would under the conditions assumed be five minutes. ihese time distances are of course merely illustrative and may be varied in practicing the invention.

Ope)ation -Fig. 3 (Method) .-As already pointed out the underlying principle of the present invention resides in the maneuvering of an airplane, after the pilot thereof is called from a holding stack, in such manner that he will have completed his holding loop at a moment which was predetermined either at or immediately after he was called from the holding stack. Let us assume that there is an airplane circling in the holding stack SI (Fig. 3) and that an operator on the ground through the medium of suitable com municating methods, such as the waving of an arm or a radio telephone conversation, or other electronic communication, determines that an airplane shall start a landing maneuver and shall reach an approach landing position five minutes hence so as to be ready to make a landing on the runway RWi at the proper time.

Let us also assume that the operator calls thepilot for a landing maneuver when his airplane is flying over the radio beacon BB3 in the direction of the arrows (Fig. 3). Let us also assume that the operator does not know where the airplane is then located except for altitude. Even though the operator may not be able to judge in what part of the holding stack the airplane is located the pilot will communicate to the operator the instant that he flies over the exit point corresponding to the radio beacon RBI. Two minutes will thus have elapsed in the meantime. The operator, after subtracting the stack loss time of two minutes plus one minute turn time (to be consumed in the holding loop) from the total time (5 minutes) he had in mind, will now inform the pilot that he is to make a holding loop having an out-time OT of one minute. This is arrived at by dividing the total time, minus the stack-loss time plus turn, by two, namely, 5(2+1) /2=1.

The pilot will as he flies over a point corresponding to the radio beacon RBI continue straight ahead for one minute after which he will make a semi-circular turn l'l (Fig. 3) of one minute and then fly straight toward beacon BB2 so that he will pass over the location of beacon RBZ at the expiration of the five-minute period set up by the operator, after which the pilot will glide toward the ground and make his landing on the runway RWl. This continuing straight ahead flying may be done by the aid of a magnetic compass, by reference to landmarks or by homing on a radio beacon, such as beacon R136 for the out-flying and such as beacons BB2 and BB3 for the in-fiying.

Let us now assume that under similar conditions the pilot is called from the stack S! for a landing procedure when he is just about to pass the point corresponding to the radio beacon RB! It will immediately become apparent that in this case the pilot will have lost no time in the holding stack Si (stack-loss time is zero) and when he reports his flying over this point the operator will then inform the pilot that he is to continue straight ahead for an out-time of two minutes as a result of which the airplane will pass over the location of radio beacon BB2 at the expiration of the total five-minute period.

Let us now assume that there is a head wind (wind from the north) or 30 miles per hour and that an airplane was located over radio beacon BB3 when its pilot was called for a landing. In this case in addition to the regular two minutes stack loss time, that would occur under no-Wind condition, the airplane will have been blown back /13:, minute distance (assuming an airplane airspeed of 155 MPH.) while it made its semi-circle at beacon BB3, so that it will have yet 1 4- 95 minute distance to fly at 5 part of its original speed, making the stack-loss time 1+1.57 minutes. The net result is that approximately 2.57 minutes have elapsed when the pilot reports over beacon RBI. The holding loop time is therefore 2A3 minutes of which one minute will be consumed while making the semi-circle turn. The out-time OT plus the in-time IT is therefore 1.43 minutes. During the making of the turn in the holding loop the airplane is blown back onehalf mile during the one-minute turn time in that the wind from the north has been assumed to be a 30 MPH. Wind. At M.P.I-I. it takes times or .285 minute to lose the time gained by the wind blowing the airplane back during the turn. If we now subtract this time 0.285 minute from the total OT+IT time of 1.43 minutes we have left 1.145 minutes which is the in-time IT plus partial out-time OT (that portion of the cut-time which has the same physical distance which the in-time has). The in-time will therefore be 1.145 times 5/2 which is 0.445 minute and the out-time will be 1.145 times its-a4 plus the above 0.285 minute which equals 0.7 plus 0.285 or .985 minute. Converting this to seconds the in-time IT is 27 seconds and the out-- time OT is 59 seconds. If now for checking purposes we add the stack-loss time of 2 minutes and 34 seconds, the circle time of one minute,-

the out-time OT of 59 seconds, and the in-time IT of 27 seconds, we get a total of 5 minutes which was the total time assumed for the entire landing maneuver.

In practicing the invention without the employment of a suitable computer such as hereinafter described, the operator will use rapid mental calculation methods including the memorizing of basic relationships between wind conditions and out-time factors so that these calculations can be carried out in the mind of the operator very quickly. If theradio beacon RBB or a similarly located land-mark is used side winds will have little eflect and may be disregarded.

The applicant has thus devised a method of landing airplanes which are flying indiscriminately in the holding stack and at diiferent altitudes. By this method he will be able to cause these airplanes to land successively time-spaced apart any particular time interval which affords the necessary margins of safety by merely calling these airplanes successively at similarly spaced time intervals and by instructing each pilot at the moment he leaves the holding stack and enters the holding loop as to how much time has to 'be consumed to the point where he is to make the semi-circular turn in the holding loop, or he may advise him to turn when this out-time has been consumed. By this method of airplane landing in which airplanes are called sequentially at equal or unequal time spaced intervals these airplanes will land on the runway at substantially the same time spaced sequence in which they were called. In other words, indis criminate and haphazard distribution of airspaced and orderly distribution of airplanes.

It may be pointed out that even if the total time to be consumed in the holding stack and holding loop is five minutes, as above explained, airplanes may be called at intervals of say, two minutes so that their maneuvering in different altitudes toward an approach landing position may take place in overlapped relation without any danger of two airplanes colliding in mid-air. This is true because time spacing between airplanes is determined by the order and time spacing in which they are called whereas vertical spacing of these airplanes in different altitudes is supervised by allowing an airplane to descend to the next lower level only when such lower level has been vacated. In this connection it may be pointed out that it is assumed the airplanes are authorized to fly in different levels in the holding stack and the holding loop, said levels being spaced substantially 500 feet apart, suitable altitude indicators or altimeters preferably being pIO- vided on the instrument board to assure each pilot as to the altitude at which he is flying. Other altitude spacings may obviously be used.

Although in the above operation it was assumed that the pilot was guided by radio beacons, it should be understood that he may be guided by other land-marks and that these beacons are not necessary elements of the present invention, except where blind landings are contemplated.

The applicant has thus devised a method of airplane landing which causes airplanes to land in the same time spaced sequence as these airplanes are called from the holding stack irrespective of the positions these various airplanes occupy in the stack at the time they are being called for landing maneuvers. In this connection if an air plane for some reason or another fails to make his landing he will be instructed to fly into a specifled altitude in the holding stack and await his turn to land. He will in time be laddered down and eventually be told to start his landing procedure for the second time.

Structure-Figs. 1 and 2.-In Fig. 1 has been illustrated a plan view of a landing field together with an imaginary holding stack S2 and associated holding loops L2 of various sizes and configurations. In this form of the invention it is not only necessary to inform the pilot when his out-time OT has been consumed as was the case in the oblong holding loop of Fig. 3, but in this form of the invention the pilot is informed as to the angle with respect to due north (azimuth angle) at which he is to fly his airplane in a straight line when he commences his holding loop maneuver.

Although the invention employing a holding stack and holding loops of the configuration illustrated in Fig. 1 may be practiced without the actual employment of radio beacons, radio beacons BB4 and BB5 illustrated are preferably used and they are preferably of the same construction as those illustrated in Fig. 3 of the drawings and heretofore described.

Opc2-ation-Figs. 1 and 3 (Method).Let us assume that one or more airplanes are flying at different altitudes, and in the direction of the arrows, in the holding stack S2 (Fig. l) and that an operator in a ground located tower by suitable communication means, such as a radio telephone, calls an airplane from this holding stack S2 by informing the pilot of such airplane that he is to get into an approach position over a point corresponding to the radio beacon BB4. Let use assume that he is to arrive at such approach position five and one-half minutes after he has been called but he is not informed of this fact.

Let us first assume that the airplane is directly over the point corresponding to the radio beacon R135 when he is called for a landing maneuver. Since all of the turns illustrated in Fig. 1 may be assumed to be one minute semi-circles and since the straight portions of the holding stack may be assumed to be distances requiring one and one-half minute of flying time, assuming no wind, it becomes immediately apparent that two and one-half minutes will be consumed by the pilot in the holding stack. This losttime, for con venience, may becalledthe stack-loss time. As

the airplane leaves the holding stack S2 at the point corresponding to radio beacon RB4, the pilot will report to the operator of his reaching the exit point of the holding stack. The operator will then quickly subtract this stack-loss time from four and one-half minutes (the total time of five and one-half minutes minus the semi-circle time of one minute in the holding loop) after which he will divide the remainder by two (all in his mind) which will be the out-time OTI (Fig. l) the pilot must consume in flying in a straight line. This out-time as is readily determined is one minute. The operator will previously have qualifled himself, as by memorizing numerous related out-times and angles, to arrive at the value of the angle at which the airplane must fly from the exit point RB i and will inform the pilot as to this angle. As can be easily verified this angle al will be approximately 36. The operator will also keep track of time and will inform the pilot at the expiration of the one minute period to make a right-hand one minute procedure turn and head back toward the exit point BB4 of the holding stack. It is readily understood that the airplane will reach this point at substantially the expiration of the original five and one-half minute period mentioned.

Had the airplane been located at the point [2 in the holding stack S2 (Fig. 1) he would have immediately, upon being called, started a one minute semi-circle, as shown by dotted line 34, so that he would have passed the exit point of the holding stack S2 exactly one minute after having been called. As he reports his exiting from, or leaving of, the holding stack to the operator the operator will observe that the stack-loss time is one minute and by subtracting this one minute from four and one-half minutes and dividing the difference by tWo he will know that the out-time 0T2 will be one minute and 45 seconds. The operator will from this out-time of one and three-fourth minutes quickly inform the pilot that he is to make an angle corresponding to an outtime of one minute and 45 seconds which angle a2 is aproximately 20. Which angle would be called 340 azimuth.

In calculating this out-time the fact that the so-called semi-circle is actually more than a semi-circle has been disregarded. This will be more fully discussed hereinafter.

The pilot will then fly along the out-time line 0T2 (20 to left due north) and will be informed by the operator at the expiration of one minute and 45 seconds period'that he is to make a righthand semi-circular one-minute procedure turn, after which the pilot will home toward the loop exit point R134 and will reach this point substantially five and one-half minutes after he was called by the operator to make a landing maneuver.

Ifwe now assume that an airplane is just about to pass the exit point when its pilot is called by the operator he will immediately report back to the operator that he is exiting from the holding stack and the operator will then know that the entire five and one-half minutes must be expended in the holding loop. The operator will then divide four and one-half minutes (circle time being omitted) by two giving him an outtime 0T3 of two and one-fourth minutes. The operator will then inform the pilot that he is to head out into space at an angle a3 of 16 to the left of due north (34 azimuth) and that he shall make a right-hand one-minute semi-circle turn after he has flown for two minutes and 15 seconds in the instructed direction. Or the operator may call the pilot when this time has been consumed and tell him to make his procedure turn and proceed back toward lined up beacons R134 and BB5. Under this condition the airplane will consume the entire five and one-half minutes in the holding loop, the outtime T3 in this case being two minutes and seconds and the angle will be approximately 16. Under the foregoing maneuvers it was assumed not to be windy.

Under various conditions of wind the operator must modify the instructions of out-time and azimuth angle to compensate for the direction and velocity of wind. For this wind correction the wind is divided into two components one of which is a head or tail Wind and the other of which is the side-wind component which will be calculated as a drift angle. If the wind for northward flying is from the right the communicatecl angle (azimuth angle) must be increased (acute angle reduced) to the extent of the drift angle itself and also to the extent the airplane drifts during the making of its semicircular turn. This may be very easily done in the mind of the operator. Should the wind be from the west, that is, from the left, the com municated angle must be decreased (acute angle increased) to the extent of the drift angle and the semi-circular turn time drift. wind for northward flying the out-time OT must be increased by multiplying the calm weather out-time by a number greater than one whereas if this wind is a tail wind the out-time must be decreased by multiplying the calm weather outtime by a fractiondepending upon the velocity of the wind. In other words, the operator can issue approximate instructions as to the necessary landing maneuvers which are close enough to cause the landing of airplanes in substantially the same time spaced sequence as they were called from the holding stack.

Under those conditions when it is desired to call a plurality of airplanes in very close sequence, that is, call these airplanes at spaced time intervals two minutes apart where the entire landing maneuver requires live and one-half minutes it is also necessary to instruct the pilot when he may descend to the next lower altitude.

In Fig. 2 of the drawings altitudes of 1500, 2000, 2500, 3000 and 4000 feet have been illustrated. Obviously these altitude assignments are only illustrative and may be varied in practice. It will. be observed that the first airplane API to be called occupied an intermediate position in ft the holding stack S2 and for this reason was required to make a medium size holding loop, corresponding to an out-time 0T2, whereas the airplane APZ which was the second one to be called occupied a position in the holding stack so that the holding loop is of the minimum size corresponding to an out-time OT! of one minute. Also, that the third airplane AP3 to be called was almost at the exit point of the holding stack S2 when called and was therefore required to a make a maximum size holding loop having an out-time 0T3 of two minutes and 15 seconds.

It is also readily seen from Fig. 2 of the drawings that the locations of the various airplanes at the time they were called from the holding stack does not in any way affect the safety of these airplanes in that these airplanes will arrive at the point R135 for approach landing successively in the same order and time spaced relation as they were called. When airplanes are thus 10 called to make landing maneuvers in overlapped relationship they will always be called from a1- titudes in the order that they are actually stored, that is, the airplane at the lower altitude will be called first. In this connection it may be pointed out that since the airplaneAPl has already descended below the 1500 foot altitude, as shown in Fig. 2, it will so report and the operator may then instruct the pilot of the airplane APZ to descend from the 2000 foot altitude to the 1500 foot altitude and corresponding instructions will be issued to the airplane A1 3 insofar as descending from the 2500 foot to the 2000 foot altitude is concerned the moment that the pilot of the airplane APE reports having vacated the 2000 foot altitude.

It is thus seen that the method of landing airplanes embodying the present invention maintains airplanes in horizontal space separation by calling them in sequence properly time spaced and that the airplanes are maintained in vertical spaced separation by requiring them to remain at specific altitudes until they are instructed to descend to the next lower and vacant altitude. As indicated airplanes AP4 and AP5 are still in the holding stack and airplane AP4 is flying northward whereas the airplane APE is flying southward.

StructureFigs. 4, 5 and 6.-For a system employing a storage stack and a storage loop, such as illustrated in Fig. 1, and under adverse wind conditions which change from time to time, and where airplanes are to be closely and accurately time spaced, it may be desirable to have a suitable mechanical computer to 'aid the operator in determining the angle a (Fig. 1) and the out-time OT more quickly and more accurately. Since it is proposed to perform landing maneuvers by as many as three airplanes at a time in overlapped relationship, it is proposed in accordance with this form of the invention to employ a computer, or rather to employ three such computers arranged side by side which computers may be entirely independent of each '1 other but are preferably interlocked by having the cylinders 0 contained therein interconnected through the same shaft l5. Suitable couplings between shafts iii of the units may be provided if desired so that these units may be separated any desirable distance and so that they may be disconnected to allow them to be more conveniently packed during shipment. For convenience only the middle one of three such machines have been illustrated in detail in Fig. 4 and will be described in detail.

Referring to Fig. 4 the computer under consideration preferably comprises a cylinder C mounted for rotation through the medium of a shaft i5 and contained within a suitable casing (not shown in detail), the cover for which casing has been illustrated in Fig. 5 of the drawings. Athough, as more fully pointed out hereinafter, the cylinder (3 may be moved endwise such endwise movement of the cylinder is not necessary and may for the present be disregarded. As shown the right-hand end of the cylinder is provided with a scale which extends from the overbeacon time" to the end of the cylinder and on this scale are marked various and wind velocities, the numeral zero indicates no head or tail wind whereas the scale markings +10, and indicate tail winds and the scale markings +10, 20, +30, and indicate head winds. For each one of these wind or no-wind conditions there is provided'on the cylinder a chart, glued or otherwise secured to the cylinder, containing a scale running lengthwise of the cylinder which is marked in minutes and seconds. As will be more fully pointed out hereinafter, outtime OT will be read from this chart. This chart has been more accurately illustrated in Fig. 6 of the drawings.

To aid the operator in reading the chart the various like out-times are connected by lines and it will be seen that these lines are closer to each other near the bottom of the chart 22 (Fig. 6) and on the lower portion of the cylinder as illustrated in Fig. l, whereas they are farther apart at the top of the chart and near the upper portion of the roller C so that endwise movement of this of the cylinder. The average separation between the lines occurs substantially at the zero wind position on the wind scale shown in scale it.

At opposite ends of the cylinder and mounted on stationary pivots are rollers RI and R2 which support a belt or tape T on which are printed the successive minutes of an hour. This tape T is in practice long enough to allow 60 marks all separated a minute apart to be marked thereon. This tape T is not provided with hour numerals because the hour of the day will obviously be in mind of the operator or the operator refresh his memory by looking at the clock CL located in the cover K shown in Fig. 5 of the drawings. Attention is directed to the fact that the minute cylinder C will cause corresponding endwise movement of the chart holder 20 and. the chart 2! contained therein.

Operation-Figs. 1, 2, 4 and 5.Let us assume that there is an airplane located at altitude 1500 feet in the stack S2 (Fig. 1) and that the operator does not know in what part of the stack path this airplane is located, but desires to have this airplane land at six minutes after a particular hour say at 6 minutes after ten (10:06:00). Let

scales marked on the chart 22 (or cylinder 0) are I? substantially twice the length of a minute measurement on tape T. The reason for this is that automatic division by two is accomplished by properly choosing these scales. This division by two is necessary because the out-time is one-half 1 7 the sum of out-time plus in--time, since out-time and in-time are equal under no-wind condition. This scale is, however, not exactly twice such length because other factors are compensated for as more fully pointed out hereinafter.

This tape T is so located in the cabinet (not shown in full) that the tape passes back of and near the top of the opening H in the cover K, this opening I! being large enough so that the time numerals just below the tape and on the cylinder C. the tape and the angle scale may be read through this single opening. Another opening 58 is provided in the cover K which opening exposes the over-beacon time lin and that portion of the tape T which is just to the left of wind scale [6 on the cylinder 0. In the casing back of the opening I! is provided a card holder in which a card 2! may be inserted. On this card are written at the proper points for certain outtimes OT under certain weather conditions the angle a at which the pilot is to fly after leaving the exit point of the holding stack (Fig. l). The de rees written on this chart 2! are determined by calculation each time an appreciable change in wind condition takes place. or they may in fact be prepared in advance one for each combination of conditions of drift angles and head and tail winds. In order to properly coordinate any particular card with. the roller C each card is provided with an'arrow 26 which must be lined up with the V-marl 29 on. the card holder 20.

In order to more accurately read the time printed on the cylinder with respect to the time appearing on the time tape T and also to more accurateli read the heading angle a earing on the chart 2! two channel bars 23 and 24 are ref erably provided. as shown in both Fi s. 4 and 5. to constitute sliding grooves in which niece of p e glass G havin a hair line 25 en raved thereon may be slid. The manner in which this slide us also assume that it is now 9:58:00. The operator will now move his tape T until the six minute mark thereon is in line with the over-beacon time line (at the edge of band [5) which is the right-hand margin of the time chart 22 on roller C. The operator will now continually look at the clock CL and will transpose the time indicated by this clock CL upon the tape T. He will observe that according to this tape T the airplane should be called at 00 minutes and 30 seconds for it is this time 10:00:30 on tape T that coincides with the start line 35. When this time is reached on the clock the operator will call the pilot of the airplane under consideration through the medium of suitable means, such as a two-way radio telephone, and will inform him that he is to start a landing procedure. The pilot who is, without the knowledge of the operator, located at point 30 will immediately begin making a left-hand one-minute semi-circle as indicated by the dotted line 38 (Fig. l) and will after completion of this semi-circle home directly toward the radio beacon RB l. As the pilot and his airplane pass over this beacon RB-i, his automatic radio direction indicator or radio compass flips over to indicate that the radio beacon has been passed. This may also be accompanied by the lighting up of a small light on his instrument board. He is aware of x the fact that he has passed the beacon RB l. As

a result of this indication the pilot will inform the operator over this two-way communicating radio telephone that he is exiting from the holding stack.

Let us assume as would appear to be the case,

' (see 1) that this occurs exactly one minute v sary, to the pilot. in azimuth degrees, which means the number of and 30 seconds after the pilot was called to make h s landing procedure maneuver, namely, at 10:02:00. The operator will now slide the glass G so that the hair line 2-5 is directly over the 2 on tape T. The operator will now read this hair line 25 on the scale of the azimuth degrees written on the chart 2| and will read this reading. which may be interpolated by the operator when neces- This angle will be expressed degrees to the right from due north, namely. 334. in this instance. The pilot will now. as by magnetic compass, fly in the direction azimuth 334.. The operator will now by reference to hair line 25 read the time 00:01:25 on the cylinder C. signifyin an out-time of one minute and 25 seconds. The operator will of course take cognizance at the start of this out-time either by starting a stop-watch or by looking at the second hand of the clock CL.

Upon the expiration of this one-minute and 25 seconds the operator will instruct the pilot to maize a right-hand one-minute semi-circle turn. The airplane will after making this turn be substantially on the line passing through radio beacons RB and R335. The pilot has from the above consideration roughly consumed one minute and 30 seconds in the holding stack, has cnsurned one minute and 25 seconds on the OT line, or out-time line, of the holding loop, has consumed in excess of one minute during his semicircle turn because the turn was more than a semi-circle, so that at least three minutes and 55 seconds have been consumed. If we allow only one minute for the turn, this will leave him one minute and 35 seconds return-time, or intirne, which is seconds more than his out time of one minute and seconds. Therefore, if ten seconds are allowed because the turn is greater than a semi-circle the airplane will reach the radio beacon BB5 exactly five and one-half minutes after the call-time at which the pilot was called to start his landing maneuver. By careful analysis it can be shown that the distance marked X in Fig. 1 represents substantially five seconds of time under the conditions just assumed making a total of ten seconds for .X as was the case above.

In practice the lines on the chart 22, the head tail wind scale l6 on the right-handend 0 thereof, the scale on the tape T and the degrees azimuth on card 2! are so located. substantially shown, that airplanes will land in substantially the same time spaced sequence as called and furthermore a predetermined constant time interval after having been called. And this holds true under any of the wind conditions considered in that proper allowance have been provided.

The dotted line conveniently called the minimiun outtime line, on the chart 22 (Figs. 4: and. 6) indicates that for that value of outtime there is insufficient time (OT) left to make a minimum tolerated loop. This minimum loop, it will be seen, is one having a one-minute outtime (OT) for zero head-wind and zero tai1-wind conditions. it will be seen that for head-winds this minimum out-time is always greater than one minute whereas for tail-winds it is always less than one minute. If the operator finds that the pilot reports leaving the holding stack at any time which will give him an out-time to the right of this minimum loop time line 20, for the particular head-wind or tail-wind then prevailing as reflected by the turned position of his cylinder C,

he will send the pilot out on the basis of the minimum out-time of one minute, not less, and change the instructions to delay succeeding flights by a like interval, as may be done by shifting cylinder C endwise.

It will be noted from the chart as shown in Fig. 5 that the start line is a straight line for all head-winds and also for all tail-winds but that this line 35 is vertical for all tail-winds but extends farther. and farther to the left as the head wind is increased. This really amounts to saying that the total time (sum of stack-loss time and loop-loss time) under all conditions of tailwinds is five and one-half minutes whereas for every head-wind this total time is different, the greater the head-wind the greater the total time. This is necessary, or at l ast desirable. in order to allow more time for the pilot to leave the stack against a bucking wind so that there will be sufficient time left for the holding loop. In this connection it may be mentioned that in practice the minimum out-time, line 28, will never come into play unless actual wind conditions are out of harmony with the wind conditions set up in the computer. It will therefore be a warning when the out-time is near this line 28 that new adjustments for prevailing wind conditions should be made.

Let us now assume a situation where the airplane was called at 10:00:30, same as above, but where we have a head-wind of 10 miles per hour (lower edge of tape T coincident with the time numerals on the -10 wind line). Let us also assume that the stack-loss time is one minute and 30 seconds, same as above. It will be seen that the out-time from the chart (Figs. 4 and 6) is now one minute and 32 seconds and that the corresponding heading angle will be 334. This angle is the same as before but would be read off of a different card 2| which would reflect the new prevailing wind condition. In practice proper scale divisions are provided between these angle readings to afford reading intermediate angles more accurately. The in-time, it can be shown, is 00:01:19. The circle time therefore is 5.5 (l:30+1:32+1:l9) or 1:09 which allows for the value of X of Fig. l a time of four and one-half seconds. In this connection it should be understood that the holding loops can no longer be drawn on a basis of time alone unless they be drawn as shown in Fig. 7, where the circling move or turn is drawn at a point substantially half-way between the extremities of the out time line OT and the in-time line IT.

Let us now consider the advantage gained by connecting these three cylinders end-to-end and allowing for simultaneous endwise movement of these cylinders. Let us assume that an airplane landing maneuver has been set up in each of these computers 40, M and t2 and that these maneuvers were set up in this same order. Let us assume that landing times of 10:05:00, 10:08:00 and 10:10:00 were set up. That is, these times appear on the tape T at the over-beacon time line of the computers 40, 4t and respectively. Let us assume that the first airplane reports safe landing before the order to turn has been given to the pilots of the other two airplanes and that the first airplane passed over the beacon RB l in its flight toward the runway at 10:05:30. The operator of computer All will then shift his cylinder C endwise to bring the over-beacon line on 10:05:30. This will cause the other two cylinders C to be moved toward the left as a result of which lower out-times for the second and third airplane will result, so that all airplanes will land 30 seconds earlier than was anticipated. The shifting of the cylinders toward the left, or to the right, in the same direction several times in succession due to early or late landing is a manifestation that the wind factors set up in the computers are not in agreement with actual wind conditions and that the cylinders 0 must be resetand a new chart 2! must be inserted in the chart holders 20.

The applicant has devised a method of airplane landing and certain instrumentalities which, if used, render the method somewhat more easily and accurately carried out, it should be understood, however, that even though only a few specific applications of the method been given there are many other sizes and shapes of holding stacks and holding loops in connection with whichthe invention be practiced, and it should be understood that various changes and modifications in the shapes of these stacks 15 and loops and the computer and other apparatus that may be used in practicing the method may be made without departing from the spirit or scope of the invention, except as demanded by the scope of the following claims What I claim as new is:

1. In a computer for computing the time an airplane is to consume in a variable length holding loop adjacent a holding stack comprising; a chart of which one extremity manifests the over-beacon time; a tape having equally spaced time intervals marked thereon and movable relative to said chart so that a predetermined overbeacon time on said tape may be aligned with such extremity; a mark on such chart lined up with the time indication on such tape when a pilot is to be called to start a landing procedure which is to be completed at the over-beacon time indicated by said tape; and a scale marking on said chart which if read directly aligned with the time on the tape when the pilot reports passing over the beacon in flying out of the holding stack and into the holding loop, indicates a time which determines how large such holding loop must be made in order for the airplane to reach the over-beacon location a second time at the over-beacon time indicated on said tape.

2. In a computer for computing the time an airplane is to consume in a variable length holding loop adjacent a holding stack dependent on the prevailing head or tail wind comprising; a chart of which one extremity manifests the overbeacon time; a tape having equally spaced time intervals marked thereon and movable relative to said chart so that a predetermined overbeacon time may be aligned with such extremity; a mark on such chart lined up with the time indication on such tape when a pilot is to be called to start a landing procedure which is to be completed at the over-beacon time indicated by said tape; and a scale marking on said chart along a line identifying the prevailing head or tail wind which if read directly aligned with the time on the tape when the pilot reports passihg over the beacon, in flying out of the holding stack and into the holding loop, indicates a time which determines how large such holding loop must be made in order for the airplane to reach the over-beacon location a second time at the over-beacon time indicated on said tape.

3. In a computer for computing the time an airplane is to consume in a variable configuration holding loop adjacent a holding stack comprising, a chart of which one extremity manifests the over-beacon time, a tape having equally spaced time intervals marked thereon and movable relative to said chart so that a predetermined over-beacon time may be aligned with such extremity, a mark on such chart lined up with the time indication on such tape when a pilot is to be called to start a landing procedure which is to be completed at the over-beacon time indicated by said tape, and an angle scale marking and a time scale marking on said chart which indicate in alignment with the time on the tape when the pilot reports passing over the beacon, in flying out of the holding stack and into the holding loop, an angle and a time respectively which determine what direction and how long the airplane must fly before it turns to make a holding loop which is of such size and configuration so as to cause the airplane to reach the over-beacon location a second time at the over-beacon time indicated on said-tape.

4. In a computer for computing the time an airplane is to consume in a variable configuration holding loop adjacent a holding stack under various side wind conditions comprising; a chart of which one extremity manifests the over-beacon til re; a tape having equally spaced time intervals marked thereon and movable rel ative to said chart so that a predetermined ovcrbeacon time ma be aligned with such extremity; a mark on such chart lined up with the time indication on such tape when a pilot is to be called to start a landing procedure which is to be completed at the over-beacon time indicated by said tape; an angle scale associated with said chart; time scale on said chart; and means indicating points of alignment on said scales with the time on the tape when the pilot reports passing over the beacon, in of the holding stack and into the hol lg loop, for reading an angle and. a time respectively which determine what direction how long the airplane must fly before it turns to make a holding loop which is of such size and configuration as to cause the airplane to reach the over-beacon location a second time at the over" beacon time indicated on said tape, there being a plurality of such angle scales and only the angle scale corresponding to the prevailing side wind must be read.

5. In a computer for computing the time an airplane is to consi he in a variable configuration holding loop adjacent a holding stack under various side wind and head and tail wind conditions comprising, a chart of which one extremity manifests the over-beacon time, a tape having equally spaced time intervals marked thereon and movable relati e to said chart so that a predetermined ovcr beacon time may aligned with such extremity, a mark on such chart lined up with the time indication on said tape when a pilot is to be called to start a landing procedure which is to be completed the over-beacon time indicated on said tape, an angle scale associated with said chart. a time scale on said chart, and means indicating points of alignment on said scales with the time on the tape when the pilot reports passing over the beacon in flying out of the holding stack and into the holding loop at which points are indicated an angle and a time respectively which termine what direction and how lon the airplane must fly before e a holding it turns to me loop which is of such size and configuration to cause the airplane to reach the over-bcacon location a second time at the over-beacon time indicated on said tape, there being a plurality of such angle scales and time scales and only the angle scale corresponding to prevailing side wind and the time scale corresponding to the prevailing head or tail wind must be read.

6. In a computer for computing the time an airplane is to fly in a variable length holding loop after leaving a holding stack so as to reach a holding position at a predetermined time com prising; a chart of which one extremity manifests the over-beacon time at which an airplane is to reach a landing position; a tape having evenly spaced time intervals marked thereon and movable relative to said chart so that a pre determined over-beacon time on said tape may be aligned with such extremity; a mark on said chart to identify the time on such tape at which a pilot is to be called to start a landing maneuver which is to be completed at such over-beacon time; and a time scale on said chart, which if read directly in alignment with the time on said tape when the pilot reports entering the holding loop, will indicate the out-time which must elapse between entering the holding loop and making a semicircular turn and which is such as to cause the pilot to complete his holding loop and reach said landing position at the expiration of said predetermined time as a result of which he will reach said landing position at said over-beacon time.

'7. In a computer for computing the time an airplane is to fly out in a variable length holding loop after leaving a holding stack and before making a turn and the azimuth angle at which such airplane is to fly comprising; a chart of which one extremity manifests the over-beacon time at which an airplane is to reach a landing position; a tape having evenly spaced time intervals marked thereon and movable relative to said chart so that a predetermined over-beacon time on said tape may be aligned with such extremity; a mark on said chart to identify the time on such tape at which a pilot is to be called to start a landing maneuver which is to be completed at such over-beacon time; a scale of azimuth angles fixed relatively to said chart which if read directly in alignment with the time on said tape when the pilot enters the holding loop will give the azimuth angle at which the pilot must fly; and a time scale on said chart which if read directly in alignment with the time on said tape when the pilot enters the holding loop will indicate the out-time which must elapse between entering the holding loop and making a semicircular turn to cause the pilot to complete his holding loop at the proper point at the expiration of a predetermined time commensurate with the distance on said tape between the starting time line and the over-beacon time line.

8. In a computer for calculating certain factors involved in providing equally spaced planes in a landing approach for planes flying at a preselected speed with random spacing in a holding stack of defined limits forming a part of a flight procedure pattern including a holding loop having different lengths dependent upon different flight conditions, time indicating means operative to represent currently elapsing time and having a time scale thereon, setting means movable relative to said indicating means and its time scale to indicate the starting time for a plane in the stack to begin an approach landing procedure including the leaving of the stack at a particular reference point, an out-time scale associated with said setting means for indicating the different values one portion of said holding loop may have for the difierent times required by planes in different portions of said stack to reach said reference point, and means movable relative to said time indicating means to a position to indicate on its time scale the time a 18 plane leaves said stack at said reference point, said means also being movable relative to said out-time scale to a position to indicate the particular value of the out-time for the holding loop required for that plane.

9. In a multiple computing organization including a plurality of computer units for calculating certain factors involved in providing equally spaced planes in a landing approach for planes flying at a particular speed but with random spacing in a holding stack of defined limits forming a part of a flight procedure pattern including a holding loop having variable lengths dependent upon different flight conditions, time indicating means operative to represent currently elapsing time and having a time scale thereon, setting means movable relative to said indicating means and its time scale to indicate the starting time for a plane in the stack to begin an approach landing procedure including the leaving of the stack at a particular reference point and also indicating the calculated time of completion of the holding loop by a plane, an out-time scale associated with said setting means for indicating the different values one portion of said holding loop may have for the different times required by planes in difierent portions of said stack to reach said reference point, means operated to a position on said time scale to indicate the time a plane leaves said stack at said reference point and at the same time being so positioned with respect to said out-time scale as to indicate the particular value of the out-time for the holding loop required for that plane, and means interconnecting said setting means of said different computer units causing the positioning of each of said setting means to a new position when any one is moved to a new position to indicate the actual time of completion of the holding loop by a plane if it differs from the calculated time at which such unit was originally set, whereby all computer units are simultaneously set in accordance with the actual flight conditions.

SAMUEL P. SAINT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,034,189 Hogan Mar. 17, 1936 2,268,240 Brixner Dec. 30, 1941 2,344,760 Wight et a1. Mar. 21, 1944 FOREIGN PATENTS Number Country Date 452,655 Great Britain Aug. 22, 1936 

